As known, isothermal or pseudo-isothermal chemical reactors are provided with an internal heat exchanger, adapted to provide to or remove heat from the chemical reaction which is generated in the reactor itself. The heat exchanger, usually, is inserted into a catalytic layer inside the reaction zone, and serves to keep the temperature of the reactants within an ideal range compensating the production (or absorption) of heat of the reaction itself. Among other uses, isothermal reactors are widely common in the plants for the production of methanol, whose synthesis reaction is exothermal.
The abovementioned reactors are of various types, for example axial, radial or combined flow, depending on the path through which the reactants pass with respect to the main axis of the reactor.
The radial or axial/radial flow isothermal reactors, in particular, are generally arranged as a pressure vessel, wherein a catalytic cartridge is accommodated, delimitated by two perforated coaxial walls and containing a suitable catalyser (catalytic bed).
In the above chemical reactors, it is also known to provide a plate heat exchanger, in which the heat exchange elements are represented by box-shaped, flattened parallelepiped elements, known as “plates”. The plates are essentially made up of two rectangular walls, connected to each other at least along the perimeter, to define an internal chamber for the passage of a heating or cooling fluid. A chemical reactor provided with a plate heat exchanger, or more simply a plate reactor, is known for example from EP-A-1284813.
Plate reactors are widely appreciated because of easy construction, easy installation even in pre-existing reactors, large heat exchange surface compared to the dimensions, which in many applications makes them preferable to reactors with tube exchangers. It is also known to perform a revamping by arranging a new plate exchanger inside a pre-existing reactor, replacing a tube exchanger.
The technique of plate reactors is confronted with the problem of adequately support the heat exchange plates, that is the abovementioned box-shaped bodies, inside the reactor.
A plate support system must meet various requirements, among which; supporting the weight of the plates in an adequate manner; guarantee reliability over time, for example concerning the vibrations caused by the reactant/product flow and which could jeopardise the physical soundness of the exchanger; provide the possibility to remove single plates or groups of plates for maintenance or replacement.
In addition, the plate support system is subjected to constructional and executive restraints due to the accommodation within a chemical reactor, where the available space is limited and accessibility might be complicated. Bulky supports can be unacceptable for example because they lower the volume available to the reaction and/or they decrease the loading/unloading capacity of the catalyst. Even more importantly, when intervening on an existing reactor and already used over a long period of time, welding operations to provide new supports are not recommendable, and one should try to use the existing ones.
Generally, there is provided a circumferential support made up of a bracket welded onto the internal edge of the cylindrical shell of the reactor, at the inlet wall of the catalytic bed, while no support is provided further inside, especially in old reactors. In other cases, the plate exchanger lies on transversal support beams, for example C-shaped or double C-shaped beams, welded inside the reactor. It should be observed that in vertical axis reactors, these supports are disposed near the lower end plate, thus not easily accessible.
Usually, the heat exchanger comprises a given number of modular elements of plate packs, each forming a section of the annular body of the exchanger. Modular construction is advantageous especially for mounting into a reactor with a partial opening, which does not allow insertion of the complete exchanger. In such cases, mounting of the exchanger inside the reactor (or replacement of the existing exchanger) is carried out by inserting the plate packs one by one, and there arises the problem of restoring the mechanical unity of the exchanger to ensure safe support and prevent the plates from shifting from the mounting position, especially when only the abovementioned external circumferential support (bracket) is available.
The known support systems need improvement to meet the requirements mentioned beforehand. In particular, known systems do not meet the requirement of total restoration of the monolithic structure of the modular exchangers, upon completion of mounting operations inside the reactor.